Occasionally a thought will enter my mind of something that I think might be useful for other engineers. Even the most experienced engineers make silly mistakes at times, so even a simple tip can sometimes have profound impact. With this in mind I have decided to make posts of such thoughts when they occur (assuming I remember them when I get to my computer!). This is the first such post.
A few years ago a friend of mine bought one of my JC1272 preamps and then called me a few weeks later asking if the distortion he was getting from it was normal. The input meter on the track he was recording to wasn't hitting red, yet he was getting audible distortion on louder passages.
Now this dude is a talented musician and producer, but not the most at home turning knobs (as he will freely admit), so I began to ask questions to try to help determine what was causing the problem. Basically, it came down to this: he was setting gain for the mic preamp with a compressor engaged between the preamp output and the A/D input. When I asked him to bypass the compressor his level pegged the meter -- clearly the thing was putting out a great deal of level (as it turns out he was actually overloading the signal path of the compressor, not the mic preamp). Yet with the compressor engaged it was reducing the level (as a compressor does), and its output was below the headroom of the converter, so it looked to him like he had plenty of headroom.
Don't laugh, we've all been guilty of goofy stuff like this, but, FWIW, make sure you set your gain with no dynamics processing engaged, or you simply may not know what's actually happening with respect to your levels. In fact, I prefer not to have a physical processor in line at all between the mic preamp and A/D input until I've got my levels. Then I'll physically insert a compressor (or EQ) and adjust it as desired. Some processors (such as Urei's much beloved 1176) can be 'bypassed', yet the input/output controls still affect the signal. With level manipulation happening in other areas of your signal path it is rather pointless to try to set optimum gain at the mic preamp, so remove all that other stuff, get your gain settings happening, and then insert and set your processing. Doing so will result in distortion-free audio and a lower noise floor.
More drum stuff coming shortly...
Thanks for reading!